The present invention relates to a method of controlling a full-electric power steering apparatus and, more particularly, to a method of determining an overload.
In a conventional overload determining method, an overload is determined when a motor current exceeds a predetermined value throughout the entire region of a steering wheel (a region from a left maximum angle to a right maximum angle of the steering wheel), and a current value is limited when an overload determined state continues over a predetermined time period. The current value is limited in order to protect a transistor for driving a motor from thermal destruction. In this case, an overload is a state wherein a motor current exceeds 38 A, and a limited current value is, e.g., 15 A when an overload state continues over a predetermined time period.
As described above, in conventional overload determination, a determination method is unchanged throughout the entire region of a steering wheel. Therefore, a current value is limited in a stopper region of a steering wheel (i.e., at the left and right maximum angles of the steering wheel and a region close thereto) when an overload state continues over a predetermined time period, thereby effectively protecting the transistor for driving a motor from thermal destruction as described above. The current value, however, is similarly limited in a normal region of a steering wheel (a region of the steering wheel except for the above stopper region). As a result, a steering wheel becomes heavy even while it is operated.
Therefore, a method in which a predetermined time period for determining the overload state is properly set so as not to limit a current in the normal region is proposed on the basis of the fact that the overload state continues for a long time period in the stopper region of a steering wheel but does not continue for long in its normal region. Since, however, this method has a problem in its correctness in operation, current limitation cannot be correctly prevented in the normal region.